Manufacture of paper products from fibers wet spun from polymer blends



United States Patent 9 i 3,047,456 MANUFACTURE OF PAPER PRODUCTS FROMFIBERS WET SPUN FROM POLYMER BLENDS Pompelio A. Ucci and Nealie T.Anderson, Decatur, Ala,

assignors, by mesne assignments, to Monsanto Chemical Company, St.Louis, Mo., a corporation of Delaware No Drawing. Filed Aug. 10, 1959,Ser. No. 832,466

11 Claims. (Cl. 162-157) This invention relates to the manufacture ofpaper, nonwoven products and the like comprising randomly intermingleddiscontinuous fibers which are at least in part composed of highlyfibrillated fibers wet spun from a blend of polymers. More particularly,the invention relates to the manufacture of paper products composed ofhighly fibrillated thermoplastic fibers wet spun from a blend ofpolymers comprising a long chain synthetic polymer from which an acrylicfiber can be formed and a cellulose ester polymer of the fiber-formingtype.

The following flow diagram is given in order that the understanding ofthe method of the present invention can be better facilitated:

Preparing wet spun fibers from a physical blend of an aerylonitrilepolymer and cellulose fatty acid ester.

I Beating the fibers to fibrillate same Sheeting out the beaten fibersinto an article Drying the article to produce a paper product In thenormal manufacture of paper, natural unmodified cellulosic fibers suchas those derived from wood pulp and other natural cellulosic fibers ofsimilar properties are beaten in an aqueous medium to disperse thefibers therein and to reduce th em to a length and fineness suitable foruse in paper making in a conventional manner. During the beatingoperation these cellulosic fibers fibrillate, the fibrillationmanifesting itself by a fraying of the surfaces and ends of the fibersto produce minute tendrils or fibrils which serve subsequently tointerlock the fibers together when they are deposited on the formingscreen of a paper-making machine to make a sheet therefrom and dried.The interlocking of these fibrils projecting from the deposited fibersimparts coherency and strength to the paper. In other words, thestrength of the paper is attained through the interlocking of largenumbers of fiber branches or fibrils during sheet formation and dry- Itwas only recently possible to manufacture sufiiciently strong papercontaining 100% synthetic hydrophobic fibers which are arrangedheterogeneously as in the case of ordinary paper made from naturalcellulosic fibers. The drawback to the utilization of said syntheticfibers has been due to the fact that it previously was regarded thatsynthetic or artificially formed fibers do not fibrillate satisfactorilywhen they are beaten in water. Prior efforts, therefore, toward theutilization of these synthetic fibers have been directed to producingpaper or non-Woven structures therefrom by effecting fiber bonding invarious manner-s. One way to effect fiber bonding involves theapplication of heat and pressure to soften and fuse the Fer-tented July31, 1982 fibers together. The fiber bonding can be achieved also by theinorganic salt fiber fusion method which requires the use of inorganicchemicals to swell the fiber surface in conjunction with heat and/ orpressure. A further method of effecting fiber bonding of synthetic fiberis by the organic solvent fiber fusion technique wherein the fibers areswollen by or partially dissolved in the solvent. Moreover, the fiberscan be bonded by the use of adhesives. Each of these methods hasinherent disadvantages and deficiencies in regard to the specificmanufacturing steps involved and to the ultimate products. Furthermore,some attempts have been made to prepare paper from a mixture of naturalcellulosic fibers and varying amounts of regenerated cellulosic fibersand/or cellulose ester fibers. Webs formed from a blend of these fibersare treated with a solvent or heat, or in some cases both to cause thefibers to coalesce. This treatment, as well as other prior methods whichserve to bind the fibers together, is costly and difficult to control.

However, some recent developments in the paper-making art have openedinteresting aspects as to the utilization of synthetically formed fibersin the manufacture of paper products and the like without recourse tothe use of adhesives and expensive bonding procedures. A familiarprocedure for manufacturing water-laid Webs, including paper, fromsynthetic fibers without the use of bonding chemicals and the likeinvolves beating wet spun fibers of acrylic polymers, viz., polymersmade from polymerized acrylonitrile or a copolymerized mixture ofacrylonitrile and up to about 15 percent by weight of another monomercopolymerizable therewith, in an aqueous suspension until the fibershave fibrillated to a sufficient extent. According to this knownprocedure the thus-fibrillated fibers formed from the acrylic polymerare deposited on a screen, for instance, to form a web with heatsubsequently being applied to the web thereby to dry and develop aninterlocking of the fibers. In the known procedure for making paperproducts from wet-spun acrylic fibers when the fibers regarded asnon-fibrillatable are combined with wet-spun acrylic fibers and beatenin aqueous suspension for an extended time, the sheets formed are soweak that in many instances they cannot be removed from the sheeting outmeans. Specifically, when polymeric ethylene terephthalate fibers, nylonfibers, cellulose acetate fibers, vinyl chloride fiber and the like arebeaten with wet-spun acrylic fibers, examination of the beaten fibersunder a microscope shows that no significant fibrillation takes place onthese fibers, excluding the wet-spun acrylic fibers which, of course,are fibrillated. Hence, the addition of non-fibrillatable fibers towet-spun acrylic fibers for the production of water-laid webs therefromimpairs the wanted properties of the synthetic fiber paper as the samehas drawbacks, including greatly reduced strength, resistance to tearand burst, and the like. While this recent disclosure represents anotable advance in the art, it is desirable to improve the strength andthe resistance to tearing and burst, shrinkage and stretchability,electrical performance, and other physical properties in both the dryand wet states of paper made from synthetic fibers.

One object of this invention is to provide a highly fibrillated fiberformed by Wet-spinning a blend of polymers comprising a long chainsynthetic polymer from which an acrylic fiber can be formed and acellulose ester polymer of the fiber-forming type. Another object is toprovide paper products and the like exhibiting improved and valuablephysical properties. A further object is to provide a method of makingsaid paper products wherein the material costs and processing costs areappreciably lower, the reduction in cost and improvements in physicalproperties opening new fields for the application of syntheticfiber-containing-paper. Other objects 3 and advantages will becomeapparent from the following detailed description of the invention.

Briefly stated, it has been found that a highly fibrillatable fiberproviding strong paper products and the like is obtained by blending abase acrylonitrile polymer, i.e., along chain synthetic polymer fromwhich an acrylic textile fiber can be formed and containing at least 85percent by weight of combined acrylonitrile with from 5 to about 25percent by the weight of the blend of a modifying cellulose esterpolymer of the fiber-forming type, the resulting blend being capable offorming a solution of at least 5 percent concentration of weight in N,N-dimethylacetamide, and by processing the resulting solution into fibersby conventional Wet spinning procedures. In the wet spinning method theblend of polymers is dissolved in a suitable solvent, such asN,N-dimethylacetamide, N,N-dimethylformamide or the like and thesolution is extruded through small orifices in a spinneret into a liquidin which the solvent dissolves but in which the polymer is insoluble.The fibers are produced under conditions that they are a predeterminedpaper-making quality and are generally characterized by a valuabletendency to fibrillate when beaten in an aqueous suspension. Theseproducts are prepared by wet abrading the fibers wet-spun from the justdescribed polymer blends in an aqueous medium, depositing the abradedfibers from the medium after same are sufficiently fibrillated to obtaina satisfactory paper product, and thereafter drying the product withapplication of heat to obtain a finished paper-product. Unexpectedresults and results which could not have been foreseen are obtained inthe manufacture of paper products from fibers made from a polymer blendcontaining the composition above-described in view of the fact thatcellulose ester fibers per se, either Wet spun or dry spun, are regardedas being substantially non-fibrillating.

The polymer blends of this invention have an average specific viscosityof not less than 0.10 or greater than 0.40, calculated from conventionalviscosity measurements for 0.1 gram of the polymer blend in 100 mls., ofN,N-dimethy-lacetamide.

As just indicated the base polymer is an acrylic fiberforming sub-stanceconsisting of a long chain synthetic polymer composed of about at least85% by weight combined acrylonitrile units. Therefore, the basepolymeric material is an acrylonitrile polymer which term refers topolyacrylonitrile, including binary and ternary polymers containingabout at least 85 percent by weight of acrylonitrile combined in thepolymer molecule, or a blend comprising polyacrylonitrile or copolymerscomprising polymerized acrylonitrile with 2 to 50 percent by weight ofanother combined monomer, the blend having an overall polymerizedacrylonitrile content of about at least 85 percent by weight.

For example, the polymer may be a copolymer of from 85 to 98 percentacrylonitrile and from 2 to 15 percent of another monomer containing theO=C grouping and copolymerizable with acrylonitrile. Suitablemonoolefinic monomers include acrylic, alpha-chloroacrylic andmethacrylic acids; the acrylates, such as methylmethacrylate,ethylmethacrylate, butylmethacrylate, methoxymethyl methacrylate,betachloroethyl meth acrylate, and the corresponding esters of acrylicand alpha-chloroacrylic' acids; vinyl chloride, vinyl fluoride, vinylbromide, yinylidene chloride, l-chloro-1-bromoethylene;methacrylonitrile, acrylamide and methacrylamide; alphachloroacrylamide,or monoalkyl substitution products thereof; methyl vinyl ketone; vinylcarboxylates, such as vinyl acetate, vinyl chloroacetate, vinylpropionate, vinyl stearate; N-vinylimides, such as N-vinylphthalimideand N-vinylsuccinim-ide; methylene malonic esters; itaconic acid anditaconic esters; N-vinylcarbazole, vinyl furane; alkyl vinyl esters;vinyl sulfonic acid; ethylene alpha, beta-dicarboxylic acids and theiranhydrides or derivatives, such as diethylftunarate, diethyl maleate,diethylcitraconate, diethylmesaconate; styrene; vinyl naphthalene;vinyl-substituted tertiary heterocyclic amines, such as thevinylpyridines and alkyl-substituted vinyl-- pyridines, for example,Z-Vinylpyridine, 4-vinylpyridine,. S-methyl-Z-vinylpyridine etc.;l-vinylimidazole and alkylsubstituted l-vinylimidazoles, such as 2-, 4-,or 5-methyl-- 1-vinylimidazole, and other O=C containing poly--merizable materials.

The polymer may be a ternary interpolymer, for example, productsobtained by the interpolymerization of acrylonitrile and two or more ofany of the monomers, other than acrylonitrile, enumerated above. Morespe-- cifically, and preferably, the ternary polymer comprisesacrylonitrile, methacrylonitrile, and 2-vinylpyridine. The ternarypolymers preferably contain to 97 percent of acrylonitrile, from 1 to 10percent of a vinylpyridine or a l-vinylimidazole, and another substance,such as methacrylon-itrile or vinyl chloride.

The base polymer can be a blend of polyacrylonitrile or a binaryinterpolymer of 85 to 99 percent .by weight acrylonitrile and from 1 to15 percent of at least one other C=C containing substances with from 2to 50 percent by weight of the blend of a copolymer of from 10 to 70percent of acrylonitrile and from 30 to percent of at least one otherO:C containing, polymeriza'ble monomer. Preferable, when the basepolymeric material comprises a blend, it will be a particular blend of acopolymer of 90 to 98 percent by weight of acrylonitrile and from 2 to10 percent of another monoolenfinic monomer, such as vinyl acetate, witha sufficient amount of a copolymer of from 10 to 70 percent by weight ofacrylonitrile and from 30 to 70 percent by Weight of a vinyl-substitutedtertiary heterocyclic amine, such as vinylpyridine or l-vinylimidazole,to give a blend having an over-all vinyl-substituted tertiaryheterocyclic amine content of from 2 to 10 percent, based on the weightof the blend.

The modifying polymer of cellulose ester of the polymer blend may be anysuitable cellulose lower fatty acid ester such as, for example,cellulose acetate, cellulose propionate, cellulose acetate-formate,cellulose acetatebutyrate, and the like. The degree of substitution ofthe cellulose ester may vary, according to the particular ester utilizedand the desired effect. For example, in the case of cellulose acetate,its combined acetic acid content may be within the range from about 48.5percent to that corresponding to the normally obtainable tri-ester,namely about 61 percent, the preferred value being in the range fromabout 52 to 57 percent acetic acid. For other cellulose lower fatty acidesters, a somewhat equivalent degree of substitution is suitable.

In general, the blends of the invention are characterized by theunexpected ease of water-fibrillating of fibers produced therefrom; andpaper products formed from the fibrillated fibers exhibit improvedphysical properties.

The base acrylic polymer and the modifying cellulose ester polymer arepreferably blended by intimately mixing them in the required amountswith a common solvent with stirring to obtain a solution of the blendwhich can be spun through orifices in a conventional spinneret immersedin a coagulating bath. The physical form of the base acrylic polymer, aswell as the cellulose ester polymer, is preferably that of fine, densegrains or powder. The base polymer is soluble in N,N-dimethy1acetamide,and in blends with the modifying cellulose ester forms a solution inN,N-dimethylacetamide, which can be formed into fibers by conventionalwet spinning procedures. The blends may be prepared by forming anintimate mixture of the base acrylic polymer and modifying celluloseester polymer in N ,N-dimethylacetamide, for instance. However, thecharacteristic solubility of the base polymer in N,N-dimethylacetamidedoes not preclude the use of other solvents in which the blend of thebase polymer and cellulose ester polymer forms a solution which can beformed into fibers in preparing spinnable solutions thereof. However,one of the advantages of the blends of the invention resides in theirproperty of forming wet spinnable solutions in N,N-d-imethylacetamide, asolvent which is especially useful in large scale production of fibers.The blends may be prepared by mixing solid polymeric materials inconventional mechanical mixers in the presence of the solvent; or theycan be mixed dry and then dissolved in the selected solvent.

The spinning solution containing the polymer blend of an acrylic polymerand cellulose ester is extruded through small orifices in a spinneret;and the polymer in the extruded solution is precipitated in acoagulating bath, thereby forming continuous filaments of any desireddiameter which can later by cut into any desired lengths. Examples ofsuitable coagulating baths for wet spinning the polymer blends includemixtures of the spinning solvent and water, such as mixtures ofN,N-dimethylformamide and water and N,N-dimethylacetamide and Water.Other suitable bath compositions may also be employed.

It is known that during coagulation in a wet spinning operation there isan inward diffusion of bath liquid into the coagulating filaments, asWell as a corresponding outward movement of solvent into the bath.Ordinarily, the solvent and bath liquid interchange in such a mannerthat the resulting filaments may contain voids or unfilled spaces alongtheir lengths. Expressed another way, the filaments have a coarse,sponge-like structure that can be clearly seen with an electronmicroscope. Fibers having such structure are known as uncollapsedfibers. Ordinarily, in order to produce satisfactory textile fiberspositive steps are taken to collapse or cave in these voids in thefilaments in order to form a dense, consolidated structure, this usuallybeing accomplished by highly tensioning the filaments and drying same ata relatively high temperature under considerable pressure or by otherknown techniques, thereby to form a more compact filamentary structurehaving a low void volume. Measurements by standard methods of thedensities of uncollapsed filaments and corresponding collapsed filamentsshow a pronounced difference therebetween, the extent to which thefilament is uncollapsed or collapsed being indicated by thesemeasurements. Obviously, the densities of the collapsed filaments aregreater than the densities of corresponding uncollapsed filaments. Inaccordance with the present invention it is preferred that the densityof the fiber used to make paper products or the like be at least percentand up to about 65 percent less than the density of a correspondingcollapsed fiber.

In contrast to the prior ant teaching in regard to the requisitecollapsing of the porous fiber structure to produce a satisfactorytextile fiber, an important aspect of the present invention is based onthe discovery that if care is taken that the filaments wet spun from thepolymer blend of the instant invention are not substantially collapsedbefore they are utilized in a paper-making process, an improved papercan be made therefrom and the uncollapsed filaments can be fibrillatedreadily and easily by the same equipment and techniques and withincomparable times as the natural cellulosic fibers commonly used to makepaper. More specifically, superior fibers for use in paper-making can beproduced by spinning a water coagulable solution of a polymer blendcomposed of an acrylic fiber-forming polymer and a cellulose ester ofthe fiber-forming type in certain proportions into an aqueouscoagulating bath under controlled conditions wherein the solvent and thebath liquid interchange in such a manner to produce filaments having asponge-like or uncollapsed structure and by purifying the filaments andby partially or totally removing the water content from the filamentsWithout appreciably destroying said uncollapsed structure.

The wet spun filaments of the present invention which are produced witha view to being utilized in accordance with the invention are subjectedto a stretching operation while they are in a gel state to attain adesired attenuation and molecular orientation according to varioustechniques. The stretch given is ordinarily at least 200% at an elevatedtemperature. This stretching preferably is performed after the residualspinning solvent carried by the filaments has been reduced to not lessthan 2 percent by weight :and preferably to not more than 10 percent byweight. During the stretching the fiber may be subjected to temperaturesin the range of from C. to about 250 C. or higher as long as the porousstructure is not destroyed. The filaments may be stretched while theyare passing through a heated liquid such as water. The filaments mayalso be heated during stretching in an atmosphere of hot air or steam,which may be dry, saturated or supersaturated. In addition to thestretching operation other treating and processing steps may be giventhe coagulated filaments, such as washing, crimping, cutting and thelike. Furthermore, the water content in the filaments can be reduced bypartially or completely drying with air, steam, or the like bycentrifuging same, by use of vacuum means, and the like withoutsubstantial reduction of the propensity of the filaments to fibrillate.It should be borne in mind that a prerequisite to the best practice ofthe invention is that the uncollapsed structure of the fibers not bedestroyed before they are processed into paper and the like.

After the porous filaments have been purified and partially or totallydried they are cut to staple lengths. Fibers in length shorter or longerthan the length of ordinary staple textile fibers can be used. Whenshort fibers are used, it is possible to charge the beater quickly. Iflonger staple is employed, the fibers should be charged slowly to avoidclogging of the beater. The relationships between the count of long andshort fibers or the fibers ratio in regard to the number of thick andthin fibers (i.e., of various deniers) are governed by the desiredproperties of the ultimate product. Hence, the fibers of the presentinvention can be of any suitable denier; or a mixture of fibers ofdifferent deniers can be used. For instance, fibers having deniersbetween 0.3 to 20 or more can be employed. On the basis of the dataobtained, it has been found that best paper is produced when the blendof polymer is spun under conditions producing a high tenacity fiber.

While the fibers Wet spun from the polymer blend of an acrylicfiber-forming polymer and a cellulose ester can be used as the solefibrous material to manufacture strong sheet-like materials, it will beappreciated that such fibers may be combined with other fibrillatablefibers including synthetic, artificial and natural fibers to manufacturesatisfactory sheet-like materials. For example, the fibers of thepresent invention are compatible with natural cellulosic fibers over awide range of proportions and paper of improved physical properties isobtainable therefrom.

In accordance with the invention at least the amount of the fibers asused herein necessary for providing a desired paper product is beaten orbattered in the presence of water in acqueous suspension, whereby thefibers are fibrillated and become dispersed. Means for beating commonlyused in the paper-making art are satisfactory. Obviously, the time towhich the fibers are subjected to the beating action depends, amongother things, on the particular beater employed. Generally speaking, thefibers should be beaten sufliciently so that they become fibrillated tosuch an extent the fibrils produced will serve to interlock togethersubsequently in the paper-making process to produce a satisfactory paperproduct. Surprisingly, the uncollapsed fiber used in the present processwill fibrillate to a much greater extent and in a shorter period of timefor a given severity of beating action than collapsed fibers of likecomposition or ordinary wet-spun acrylic fibers. Thus, the uncollapsedfibers wet spun from the polymer blend herein can be subjectedcomparably to less severe beating action and yet be fibrillatedsufficiently. Avoidance of severe beating action is desirable in someinstances since a harsh beating action produces fibers of undesirablyshort lengths. Furthermore, for a given seversity of beating underconditions where collapsed wet-spun acrylic fibers of the ordinarytextile type would be comminuted or broken into undesirably shortlengths and having broom-like ends and very short fibrils along thefiber length, the uncollapsed fibers Wet spun from the polymer blend asused in the instant invention advantageously are contused with lesscutting thereof, whereby longer fibrils along the fiber length areproduced that contribute to a more tenacious interlocking of the fibersin the ultimate product.

While excessive foaming is not ordinarily encountered during beating,anti-foaming agents such as octyl alcohol and the like may be added tothe aqueous beating medium, if desired. The suspension of fibers may bemade more uniform by known suspending agents such as freshlydeacetylated Karaya gum. If such is used properly, the fibers do notsettle or fiocculate excessively and proper sheet formation isfacilitated thereby. Although not required, the fibers may be sized bythe beater addition method or water laid webs of the fibrillated fibersmay be sized. Although the additional cost may be unwarranted in someinstances, it is within the purview of the invention to use a resinoussubstance or a potentially resinous substance on the fibers or websformed from the fibers.

The beaten fibrillated fibers wet spun from the polymer blend of thepresent invention are thereafter formed into a paper product by anysuitable process. For example, such product can be formed intoself-supporting continuous webs or sheets by the use of standard papermill equipment of various types. The self-supporting paper sheet is thencarried through a drying process. The drying of the paper can be carriedout by continuously passing the paper over heated drums in a knownmanner. Also, a moving web of paper may be passed under a battery ofdrying lamps; or other heating means can be used to dry the product.

The drying temperature may be and usually is in the same rangeordinarily used for drying natural cellulosic fiber-containing paper andis determined to a considerable extent by the properties desired in theultimate paper product. The paper products herein may be dried at roomtemperature and up to the temperature at which the fiber degradesconsiderably or melts. The drying temperature affects the properties ofthe paper product. It has been found in this regard that the physicalproperties with reference to tensile strength, tear and burst resistanceusually are related directly to the drying temperature. That is to say,when a higher drying temperature is employed, one may expectimprovements in these properties. For example, properties of handsheetsdried at 70 F. are usually inferior to a second identical handsheetdried at 200 P. which in turn is usually inferior to a third identicalhandsheet dried at 400 F.

By the term paper products is meant products comprising a multiplicityof discontinuous fibers of papermaking lengths associated together toform a coherent product which may be flexible or stifi, thick or thin,soft or hard, and including sheets, boards, filters, and molded paperarticles of all kinds.

The following examples will further illustrate the practice andimprovement of the instant invention. All parts and percentages are byWeight unless otherwise indicated.

EXAMPLE I A 1 /2 lb. Valley laboratory beater was charged with 150 gramsof oriented acylic fibers in 20 liters of water (0.75 percentconsistency). The fibers were approximately 3 denier per filament cut toan average length of A" and had been prepared by wet spinning from acopolymer compound of 94.6 percent acrylonitrile and 5.4 percent vinylacetate. The fibers had little void volume therein as seen bymicroscopic examination thereof. The density of the fiber was 1.17 gramsper cubic centimeter and the fibers were commercial textile grade typeof acrylic fibers.

The severity of the beating action of the Valley beater is regulated bythe bedplate load or counterweight that urges the bedplate against therotatable beater bars. During operation of the beater the fibers aredrawn between the beater bars and bedplate by the circulatory actiontherein. The gram sample of the fibers was processed in the Valleybeater using a 12 lb. counterweight. Samples to be formed intohandsheets were taken every 10 minutes. The handsheets which weighedapproximately 2.5 grams were formed and dried by using a Noble and Woodlaboratory handsheet machine. The machine includes an 8" square mold,press rolls, and felt, as well as a steam heated drying drum with felt.The handsheets were dried supported on a wire by being passed around adrying drum at 198 F. The data of the physical properties of thesehandsheets having an average thickness of 0.008 inch are given below inTable 1. Handsheets were weighed on a weight scale basis. Physicalstrengths of the handsheets were measured on an Elmendorf tearingtester, a Mullen bursting strength tester, and a Scott model DH tensiletester, following TAPPI standards. All values were normalized to an 8" x8" hand-sheet (44 lbs. per ream, 25 x 40--500).

Ninety-nine parts of a polymer prepared by polymerizing 94.6 percentacrylonitrile and 5.4 percent vinyl acetate (base polymer) were blendedwith 1 part of cellulose acetate (modifying polymer) having a combinedacetic acid content of 52 percent. The blend was prepared by dissolvingthe base copolymer and the modifying cellulose polymer each in powderedform in N,N-dimethy1-acetamide to produce an 18 percent spinningsolution. The solution was then extruded through a spinneret into anaqueous coagulating bath containing 60 percent dimethylacetamide and 40percent water by volume maintained at a temperature of 32 C. to form ahundle of filaments. The bundle was withdrawn from the bath and given astretch of 400 percent in boiling water containing a small amount ofdimethylacetamide. Next, the filaments were partially dried by passingsame around an assembly of drying drums. When the moisture content ofthe filaments had been reduced to about 10 percent, they were withdrawnfrom the drums and cut into lengths of inch. Examination under anelectron microscope of the cut fibers revealed that the fibers wereporous, having a sponge-like structure. In other words the fiberspossessed what is known as an uncollapsed structure. These uncollapsedfibers had an average density of only 0.75 gram per cubic centimeter.

A 1 /2 lb. Valley laboratory beater was charged with a 150 gram sampleof the uncollapsed fibers in 20 liters of water. The fibers wereapproximately 3 denier. The sample was beaten in the beater using a 12lb. counterweight. Handsheet samples were taken at intervals indicatedbelow in Table 2 and handsheets were prepared as outlined in Example I.The properties also listed in the table below were measured as outlinedabove in Example I.

Table 2 Table 4 Tear Bursting Y Tensile Tear Bursting Tensile BeatingTime (mins.) (gms) (p.s.i.) Strength Beating time (mins.) (gms) (p.s.i.)Strength (lbs/in.) (lbs/in.)

40 8 1.1 0. 3 29 2 2 1.0 50 6 0.8 1.0 21 1.7 1. 4 18 2. 1.8 12 1 8 2.2EXAMPLE III cellulose acetate (modifying polymer) having a combinedacetic acid content of 52 percent, the parts being given in Table 3below. The resulting polymer blends were separately dissolved inN,N-dimethyl-acetamide to form a like number of spinning solutions, eachcontaining about 18 percent solids. The solutions Were spun into fibersin accordance with the procedure outlined in Example II to produce wetspun fibers having an uncoll-apsed structure and an average density of0.75 gram per cubic centimeter.

The fibers produced from these solutions were processed separately inthe Valley beater, again using a 12 lb. counterweight. Samples weretaken every minutes with sheets being produced in accordance with thehandsheet method described above in Example I. The physical propertiesof the handsheets are listed in the Table 3 below and were measured asoutlined in Example I.

Table 3 Blend Composition (per- Beating Tear Bursting Tensile centacrylicpercent Time (gms) (p.s.i.) Strength cellulose ester) (mins.)(lbs/in.)

The beaten fibers were examined visually under a microscope and comparedwith the beaten fibers produced in Examples I and II. For the samebeater adjustment and same beating time, the fibers of the instantexample were more pronouncedly fibrillated. That is to say, that thecount of fibrils projecting from the fiber body was greater.Furthenmore, the number of fibrils that had been severed from the bodyof the fiber of the instant example was significantly less. Thisindicated that the fibrils of the fiber beaten in accordance with theexample were tougher and adhered more tenaciously to the fiber body.

EXAMPLE IV Handshcets were prepared from collapsed fibrillated fibersWet spun from a solution of a polymer blend composed of 90 percent of acopolymer of 94.6 percent acrylonitrile and 5.4 percent vinyl acetateand 10 percent cellulose acetate having a combined acetic acid contentof 52 per-cent. The spinning conditions were similar to those used inExample II except that the fireshly spun filaments were completely driedwhile being passed around the assembly of drying drums to cause theresulting filament structure to be collapsed. The properties of thehandsheets are listed in Table 4 below and were measured as above.

It can be seen by comparing the data in Example III given :for a similarfiber acrylic polymer-l0% cellulose acetate) but uncollapsed fiber withthe data rfor the collapsed fiber of this example, that the uncollapsedfiber can be used to form the better paper.

EXAMPLE V Handsheets were prepared from uncollapsed fibril-lated fiberswet spun from a solution of a polymer blend composed of 88 percent of acopolymer of 94.6 percent acrylonitrile and 5.4 percent vinyl acetateand 12 percent cellulose acetate having a combined acetic acid contentof 60.4 percent (cellulose tri-acetate). The spinning conditions weresimilar to those used in Example II with the resulting fibers having anuncollapsed structure. The properties of the handsheets made from thesefibers are listed in Table 5 below and were measured as above.

Table 5 Tensile Beating Time (mins.) Tear Bursting Strength (E (13.8.1.)(lb./m.)

EXAMPLE VI Table 6 Tear Bursting Tensile Beating Time (mins.) (gins)(p.s.i.) Strength (lb/in.)

EXAMPLE v11 This example illustrates an attempt to form a paperhandsheet from wet spun cellulose acetate fibers, as well as a handsheetfrom a blend of Wet spun acrylic fibers and wet spun cellulose acetatefibers.

Cellulose acetate having a combined acetic acid content of 52 percentwas dissolved in N,N-dimethylacetamide in an amount sufiicient to give aresulting spinning solution of 15 percent solids. The solution wasextruded through a spinneret into a coagulating bath composed of waterand maintained at a temperature of 30 C. to form a bundle of filaments.The bundle was washed with water and given an afterstretch of percent.Next, the filaments were partially dried by being passed around anassembly of drying drums. When the filaments were dried to the pointwhere they were only slightly damp,

they were Withdrawn from the drums and cut into inch len s. The fibershad an uncollapsed structure, a tenacity of 1.3 gms./ denier, and anelongation of 5 per cent. The Valley beater above mentioned was chargedwith a 150 gram sample of these wet spun cellulose acetate fibers in 20liters of Water. The fibers were approximately 3 denier. The sampi-e wasbeaten in the beater using a 12 lb. counterweight. 'Handsheet sampleswere taken at appropriate intervalswith sheets being produced inaccordance with the hand sheet formation method described above inExample I. The physical properties of the handsheets, including tear,bursting, and tensile strength, were too low for measurement.

Eighty-five parts of the wet spun acrylic fibers produced in accordancewith Example I except that the fibers during formation were dried as inExample I l 50- that same had an uncollapsed structure was blended with15 parts of wet spun cellulose acetate fibers produced as above in thisexample. The Valley beater was charged with a 150 gram sample of theresulting fiber blend in liters of water. The same was beaten in thebeater using a 12 lb. counterweight. \Handsheet samples were taken atappropriate intervals with sheets being produced in accordance with thehandsheet formation method above described. The physical properties ofthe handsheets, including tear, bursting, and tensile strength, were toolow for measurement.

It should be understood that although the foregoing examples describe indetail some of the more specific features of the invention, they aregiven primarily for the purpose of illustration and the invention in itsbroader aspects is not limited thereto. For example, although theinvention has been illustrated in the specific examples in connectionwith the production of hand formed sheets, it is applicable tocontinuous production of paper sheets of indefinite lengths. Thus, thefibers may be beaten in a continuous manner and the resulting beatenfibers sheeted out on a Fourdrinier machine, for instance. In such case,the sheet would be dried such as by passing same over drying cans andtaken up in roll form. Likewise, when the base blending polymer madefrom other acrylonitrile polymers and when the modifying cellulose esterpolymer made from other esters of cellulose described above are used inthe manufacture of paper products, similar noteworthy improvements inregard to physical properties of the paper are obtained.

Therefore, it seen that an important aspect of the invention is based onthe discovery that fibers which have been produced by wet spinningtechniques from particular blends of polymers may be fibrillated moreeasily and to a much greater extent than ordinary wet spun acrylicfibers. Moreover, such improved fibrillation is even more significantwhen the fibers of the present invention are produced under conditionscausing a porous or 'uncollapsed structure. The number of fibrils perfiber is increased and the ease of severance of the fibrils from thefiber is reduced. Furthermore, the cost of the resulting fibers is lessexpensive.

The fibers of the present invention are particularly applicable to thepreparation of paper by the wet process or water :laid technique, bysheeting out of the beaten highly iibrillated fibers from an aqueousmedium onto a conventional paper-making machine. As indicated above,this sheeting out can be accomplished on a Fourdrinier machine.Alternatively, the fibers can be water laid on a porous frame as isemployed in the preparation of handsheets. The water can be separatedfrom the fibers by any suitable means while forming the fibers into itsdesired shape. The sheets made in any of the aforesaid ways may be justa few thousandths of an inch or several inches thick or more. Shapedpaper articles, of course, can be made by other similar methods.

Tough paper products having a substantial degree of flexibility andbeing relatively soft to the touch can be made; other products may berelatively stiff and resilicut. The products have a high resistance tobursting and tearing both in the wet and dry state. An important featureof the paper products is their inherent ability to resist the action ofcertain chemicals. The products are, in general, readily wettable havinga high strength and are porous. Filters produced from the paper hereinhave improved filtration efficiency and thus may be efficaciously usedin the manufacture of filters for cigarettes, filters for chemicalswhich do not attack the fibers under the conditions employed, andfilters for other purposes. As indicated, while excellent paper productsmay be produced without the using of bonding agents, sizes, resins,potentially resinous materials, or the like, it is understood of coursethat these can be employed also in the present process if desired.

The fiibrillated fibers produced in accordance with the instantinvention are particularly useful in blending with ordinary cellulosepulp from wood, cotton linters, and the like. For example, a papercomposed of a blend of only 10 percent of the fibers of the presentinvention with the remainder being natural unmodified cellulosic fibershas markedly superior dimensional stability, better ageing properties,etc., than paper composed 100 percent of such cellulosic fibers. In viewof these improved properties, the fibers of the present invention can beemployed advantageously as the sole type of fiber in or with a blend ofother fibers in selected paper end uses such as currency paper, abrasivepaper, tabulating card stock, photographic base stock, blueprint andsimilar stock, map and chart stock, impregnating paper, filters, and thelike.

The present invention makes possible the production of a fiber that isfeltable and eminently suitable for use in paper-making. The highlyfibrillated fiber realized in the present invention is desirable in thatthe paper products made therefrom are stronger and more able to absorbenergy without bursting. In addition, the strength arising from atenacious cohering of the fibrils to the fiber body contributessignificantly to a higher resistance to breaking upon being flexed. Theiibrillated fiber is par ticularly characterized as having been wet spunfrom blends of certain polymers and having a porous, sponglikestructure, the fibrils thereof being tough, pliable, and tenaciouslyadhered to the fiber surfaces and ends.

Since it is apparent that many changes and modifications can be made inthe above-described detailed specification without departing from thenature and spirit of the invention, it is to be understood that theinvention is not to be limited except as set forth in the appendedclaims.

What is claimed is:

1. A process for the manufacture of a paper product comprising the stepsof preparing wet spun fibers from a solution containing a physical blendof about 95 to 75 percent by weight of a base polymer of a long chainsynthetic polymer from which an acrylic textile fiber can be formed andcontaining at least percent by weight COID- bined acrylonitrile andabout 5 to 25 percent by weight of a modifying polymer of a celluloselower fatty acid ester of the fiber forming type, said blend beingcapable of forming a solution of at least 5 percent concentration byweight in N,N-dimethylacetamide, beating said fibers in an aqueousslurry to fibrillate same, sheeting out the beaten fibers into apredetermined shape and thickness, and drying the resulting sheeted outmaterial to form a strong coherent paper product.

2. The process of claim 1 wherein the base polymer in the blend is acopolymer containing at least 85 percent by weight of combinedacrylonitrile and up to 15 percent by weight of another mono-olefinicmonomer copolymerized therewith.

3. The process of claim 2 wherein the other monoolefinic monomer isvinyl acetate.

4. The process of claim 3 wherein the cellulose ester is celluloseacetate, the combined acetic acid content of which is within the rangeof 48.5 to 57 percent by weight.

5. A process for the manufacture of a paper product comprising the stepsof forming a solution from a physical blend of about 95 to 75 percent byweight of a base polymer of a long chain synthetic polymer from which anacrylic textile fiber can be formed and containing at least 85 percentby weight combined acrylonitrile and up to 15 percent by weight ofanother mono-olefinic monomer copolymerizable therewith and about to 25percent by weight of a modifying polymer of a cellulose lower fatty acidester of the fiber forming type, said blend being capable of forming asolution of at least 5 percent concentration by weight inN,N-dimethylaceta1nide, spinning the resulting solution into an aqueouscoagulating bath to produce filaments therefrom, cutting said filamentsinto short length fibers, beating said fibers in an aqueous slurry tofiibrillate same, sheeting out the beaten fibers into a predeterminedshape and thickness and drying the sheeted out material to form a strongcoherent paper product.

6. The process of claim 5 wherein the other mono-olefinic monomer isvinyl acetate.

7. The process of claim 6 wherein the cellulose ester is celluloseacetate, the combined acetic acid content of which is within the rangeof 48.5 to 57 percent.

8. The process for the manufacture of a paper product comprising thesteps of forming a solution from a physical blend of from 95 to 75percent by weight of a base polymer of a long chain synthetic polymerfrom which an acrylic textile fiber can be formed and containing atleast 85 percent by weight combined acrylonitrile and up to percent byweight of another mono-olefinic monomer copolymerizable therewith, from5 to percent by weight of a modifying polymer of cellulose lower fattyacid ester of the fiber-forming type, said blend being capable offorming a solution of at least 5 percent concentration by weight in asolvent selected from the group consisting of N,N-dimethylformamide andN,N-dimethylacetamide, spinning the resulting solution into an aqueouscoagulating bath containing a proportion of said solvent to producefilaments therefrom under conditions wherein the solvent and the bathliquid interchange to impart an uncollapsed structure to the filamentssuch that the density thereof is 15 to percent less than the density ofcorresponding collapsed filaments, stretching and puritying thefilaments, reducing the water content of the 14; filaments withoutappreciably destroying said uncollapsed structure, cutting saidfilaments into short length fibers, beating said fibers in an aqueousslurry to fibrillate same, sheeting out the beaten fibers into apredetermined shape and thickness, and drying the sheeted out materialto form a strong coherent product.

9. The process of claim 8 wherein the solvent is N,N- dimethylacetamide.

10. The process of claim 8 wherein the other monoolefinic monomer isvinyl acetate.

11. The process for the manufacture of a paper product comprising thesteps of forming a solution from a physical blend of from 95 to percentby Weight of a base copolymer of from to 98 percent by weight combinedacrylonitrile and 15 to 2 percent by Weight combined vinyl acetate andfrom 5 to 25 percent by Weight of modifying polymer of cellulose acetateof the fiber-forming type, the combined acetic acid content of which isin the range of 48.5 to 57 percent by weight, said blend being capableof forming a solution of at least 5 percent concentration by Weight inN,N-dimethylacetamide, extruding the resulting solution through orificesin a spinneret immersed in an aqueous coagulating bath containing aproportion of N,N-dimethylacetamide to produce filaments having anuncollapsed structure such that the density thereof is 15 to 65 percentless than the density of corresponding collapsed filaments, withdrawingthe filaments from the coagulating bath, passing the filaments through asecond aqueous bath maintained at a temperature in the range of 250 C.,stretching the filaments during their passage through said second bathby at least 200 percent, partially drying the filaments, cutting thefilaments into paper-making lengths, beating said fibers in an aqueousslurry to fibrillate same, sheeting out the beaten fibers from saidaqueous slurry into a predetermined shape and thickness, and heating thesheeted out material until dry to form a strong coherent product.

References Cited in the file of this patent UNITED STATES PATENTS2,736,946 Stanton et a1. Mar. 6, 1956 2,788,563 Stuchlik et a1. Apr. 16,1957 2,810,646 Wooding et al. Oct. 22, 1957 2,930,106 Wrotnowski Mar.29, 1960

1. A PROCESS FOR THE MANUFACTURE OF A PAPER PRODUCT COMPRISING THE STEPSOF PREPARING WET SPUN FIBERS FROM A SOLUTION CONTAINING A PHYSICAL BLENDOF ABOUT 95 TO 75 PERCENT BY WEIGHT OF A BASE POLYMER OF A LONG CHAINSYNTHETIC POLYMER FROM WHICH AN ACRYLIC TEXTILE FIBER CAN BE FORMED ANDCONTAINING AT LEAST 85 PERCENT BY WEIGHT COMBINED ACRYLONITRILE ANDABOUT 5 TO 25 PERCENT BY WEIGHT OF A MODIFYING POLYMER OF A CELLULOSELOWER FATTY ACID ESTER OF THE FIBER FORMING TYPE, SAID BLEND BEINGCAPABLE OF FORMING A SOLUTION OF AT LEAST 5 PERCENT CONCENTRATION BYWEIGHT IN N,N-DIMETHYLACETAMIDE BEATING SAID FIBERS IN AN AQUEOUS SLURRYTO FIBRILLATE SAME, SHEETING OUT THE BEATEN FIBERS THE RESULTING SHEETEDOUT MATERIAL TO FORM A AND DRYING THE RESULTING SHEETED OUT MATERIAL TOFORM A STRONG COHERENT PAPER PRODUCT.